The instant invention relates to flow measuring devices and more particularly to a flow measuring device for measuring the flow rate of a fluid in a partially filled conduit.
While a variety of different types of devices have been heretofore available for measuring the flow rates of fluids in conduits, most of them have only been operative for measuring fluid flow rates in entirely filled conduits. However, it has been found that in certain types of fluid systems there can also be a need for providing accurate flow measurements of fluids as they pass through partially filled conduits. For example, many gravity-fed systems, such as sewage treatment systems, comprise various lines, including inlet lines, which are normally only partially filled but which discharge or spill freely into large pools, tanks or conduits. In order to accurately monitor the flow rates of the various streams in systems of this type, it can be necessary to provide devices in the partially filled lines thereof for monitoring the flow rates in these lines. One of the most common types of heretofore-available flow measuring devices which has been utilized for applications of this type and which represents the closest prior art to the subject invention of which the applicant is aware is the Parshall flume device. A Parshall flume device consists of an open channel-like conduit having a substantially horizontal bottom wall, a pair of spaced, upstanding sidewalls which converge in a downstream direction and terminate in an open downstream end, and a pressure tap for measuring the head pressure adjacent the bottom wall. However, while it has been found that Parshall flume devices can be effectively utilized for many applications, it has also been found that they can be less than entirely effective when they are connected to tubular pipe sections of round or circular cross section. Specifically, it has been found that when fluid is transferred directly from a pipe section of circular cross section into a Parshall flume device of rectangular cross-section, irregular flow patterns and turbulence can be created in the fluid which can cause the Parshall flume device to produce inaccurate flow readings. Another type of device which has been heretofore available for measuring the flow rates of fluids in partially filled conduits is the Kennison nozzle, which comprises an elongated rounded or concave bottom wall, a pair of elongated, spaced, upwardly convex side walls which extend upwardly from the bottom wall, and a pressure tap for measuring the head pressure adjacent the bottom wall. However, it has been found that while a Kennison nozzle can be effectively connected to and utilized with a pipe section of circular cross section, a Kennison nozzle generally has a non-linear flow curve which can make flow calculations more difficult. It has also been found that the unusual interior cross-sectional configuration of a Kennison nozzle can make it difficult to inspect a device of this type to make sure that it is capable of producing accurate readings. In addition to Parshall flume devices and Kennison nozzles, other types of flow measuring devices have also been heretofore available for measuring the flow rates of fluids in partially filled conduits. However, they have generally had the same disadvantages as the Parshall flume devices and the Kennison nozzles, and hence they have also generally been less than entirely satisfactory.
The instant invention provides a device for measuring the flow rates of fluids in partially filled conduits which is simple to operate and highly effective for producing accurate flow-measurement readings. The device of the instant invention is also easy to inspect, and it is adjustable to adapt it for different flow ranges. Specifically, the device of the instant invention comprises sequentially disposed inlet, transition, and converging sections and means for determining the level of the fluid in the converging section. The inlet section is constructed so that it has a substantially circular interior cross-sectional configuration, and the converging section comprises a substantially flat bottom wall and a pair of spaced, longitudinally converging sidewalls which extend substantially perpendicularly upwardly from the bottom wall. The transition section extends between the inlet section and the converging section, and it is configured so that it provides a substantially smooth transition between the interior of the inlet section and the interior of the converging section. The transition section preferably has a length which is at least as great as one-half of the diameter of the inlet section, and the upstream end of the converging section preferably has a width which is substantially equal to the diameter of the inlet section. The sidewalls in the converging section are preferably substantially straight, and the bottom wall is preferably also substantially straight, although an upwardly inclined lip is preferably provided on the bottom wall adjacent the downstream end of the converging section. The means for determining the level in the converging section preferably comprises means for sensing the pressure in the interior of the converging section adjacent the bottom wall.
For use and operation of the flow measuring device of the instant invention, the inlet section is connected to a pipe section of substantially circular cross section so that the bottom wall of the flow measuring device is in a substantially horizontal disposition wherein the downstream end thereof is substantially unobstructed whereby a fluid can spill freely therefrom. Thereafter, when a fluid is passed through the device, the flow rate of the fluid can be accurately and effectively measured utilizing the pressure sensing means in the converging section. In this regard, since the converging section has a rectangular cross-sectional configuration, the pressure which is sensed by the pressure sensing means is directly proportional to the height of the fluid in the converging section, and this can be easily correlated to the flow rate of the fluid. Further, since the device includes a transition section which provides a smooth transition between the inlet section and the converging section, a fluid can be passed into the converging section without producing irregular flow patterns and turbulence therein. Still further, since the device preferably includes a lip on the bottom wall of the converging section adjacent the downstream end thereof, it is possible to more easily calibrate the device for zero-flow conditions. Specifically, when the flow through the device is shut off, the lip enables the device to reach a zero-flow condition without requiring that all of the residual fluids in the device and the pipe sections connected thereto be completely drained from the device. Accordingly, a zero-flow condition can be reached within a matter of minutes, whereas it might take several hours to reach a zero-flow condition with another type of flow measuring device.
One embodiment of the device of the instant invention is constructed so that it is also adjustable to increase or decrease the capacity thereof. Specifically, this embodiment of the device preferably includes removable wedge-shaped inserts which are positioned along the inner sides of the sidewalls of the converging section adjacent the downstream end thereof. The inserts are constructed so that they gradually reduce the width of the converging section by an increased amount and so that they therefore reduce the capacity of the flow measuring device. However, the inserts are constructed and secured to the sidewalls so that they are removable to increase the capacity of the device. Accordingly, the device can be installed in a system, such as a sewage treatment system, and initially operated with the inserts in place in the converging section. Thereafter, however, if it becomes necessary to increase the capacity of the system, the inserts can be removed to enable the device to operate at a higher flow range.
Accordingly, it is a primary object of the instant invention to provide an effective flow measuring device for partially filled pipe sections.
Another object of the instant invention is to provide an effective device for measuring the flow rates of fluids in partially filled pipe sections, which can be adapted to operate at different flow ranges.
A still further object of the instant invention is to provide a device for measuring the flow rates of fluids in partially filled pipe sections comprising an inlet section of substantially circular cross section, a converging section of substantially rectangular cross section, and a transition section which provides a substantially smooth transition between the inlet section and the converging section.